This invention relates to broadband wireless communications between a base station and customer sites located within a geographical area and more particularly to a cellular, broadband wireless communication system which combines multiplexing and modulation schemes to provide both low and high bandwidth service functionality.
Broadband wireless systems such as Local Multipoint Distribution Systems (LMDS), known as Local Multipoint Communication System (LMCS) in Canada, are being developed to provide point to multipoint, high bandwidth services between a base station connected to a backbone such as an asynchronous transfer mode (ATM) network and network interface units (NIUs) at fixed locations within a defined geographic area or cell. A wireless link between the base station and the NIUs operates at a wireless radio frequency (RF) typically in the 28 GHz range depending on the allocated frequency license. A transceiver at the base station and a transceiver at each NIU site supports bi-directional, broadband xe2x80x9clast milexe2x80x9d communication between a service provider and a customer.
Traditional wireless access systems employ one polarization or another (vertical or horizontal, for example) as a means for delivering services over a radio medium to a given customer(s) site. These systems tend to be optimized for specific types of services that are largely dictated by the radio licensing structure and/or regulatory requirements.
With the advent of broadband licensing (LMDS/LMCS, for example), large numbers of different service types can be offered using a common delivery infrastructure. These varying services can be low bandwidth in nature (so called POTS, T1 or E1, fractional T1 or E1, Ethernet, or other, for example) or can be high bandwidth in nature (so called T3 or E3, OC-n, or other, for example).
Typically, the low bandwidth services are more cost effectively delivered through the sharing of radio resources. Sharing radio resources can be achieved by sharing resources in time, for example, using techniques such as time-division-multiple-access, (TDMA). This technique divides a given radio communication channel up into time slots which are allocated in a fixed or dynamic manner to the various customer-site equipment which are sharing this radio channel/resource. Although this tends to be more cost effective, this type of access technique commonly employs lower efficiency modulation schemes, quadrature-phase-shift-keying (QPSK), for example, which utilize more spectrum/license.
Typically the high bandwidth services are not as cost sensitive but demand much more capacity and therefore need to be connected using high efficiency modulation techniques, quadrature-amplitude-modulation (QAM), for example. These are not amenable to radio resource sharing and therefore are more optimally run within independent radio channels. The technique of using a number of independent radio channels serving one customer site each is referred to as frequency-division-multiplexing (FDM).
International PCT application WO 97/29559 by Evans et al, published on Aug. 14, 1997, and assigned to Stanford Telecommunications, Inc. relates to a broadband wireless ATM system and in particular, discloses a protocol for effecting point-to-multipoint communications between a base station and a plurality of users. The protocol utilizes time-division multiplexing (TDM) in the direction of the base station to the users (the downstream direction) and time-division multiple access (TDMA) in the direction of the user to the base station (the upstream direction).
The downstream and upstream transmissions are carried on radio frequency (RF) waveforms by either QPSK modulation or QAM modulation but not both concurrently.
This invention is applicable to wireless multipoint access systems that employ a cellular approach to provide service coverage to fixed customer sites within a given geographical area.
This is achieved by using shared radio access techniques which optimally allow multipoint connections of low bandwidth services as well as high bandwidth services to significantly enhance the use/applicability of broadband multipoint access systems.
Generally, the system includes dual interface means associated with a base station to accommodate both low and high bandwidth services and switching means at the base station to deliver the appropriate service.
Therefore in accordance with a first aspect of the present invention there is provided a broadband wireless system comprising: a base station connected to a switched digital backbone network and having a transceiver for bi-directional digital communications over a radio frequency (RF) wireless link via radio interface means; and a network interface unit (NIU) located at a customer premise, the NIU having a transceiver for bi-directional wireless communication with the base station over the wireless link; wherein the radio interface means includes multiplexing means for both time division multiple access (TDMA) and frequency division multiplexing (FDM) and modulation means for both quadrature phase shift key (QPSK) and quadrature amplitude modulation (QAM) whereby both low and high bandwidth digital services may be provided.
In a preferred embodiment of the invention the backbone is an asynchronous transfer mode (ATM) network and the radio interface means includes a pair, or more, of ATM radio interface cards (ARICs), one of a pair for TDMA and the second of a pair for FDM.
In accordance with a second aspect of the invention there is provided a method of delivering multiple bandwidth service functions over a wireless link between a base station and a network interface unit (NIU) at a fixed customer site, the method comprising: providing radio interface means at the base station for transmitting and receiving a radio frequency signal to and from the NIU; providing time division multiple access TDMA multiplexing and quadrature phase shift key (QPSK) modulation schemes at the radio interface means for low bandwidth service connections; and providing frequency division multiplexing (FDM) and quadrature amplitude modulation (QAM) schemes at the radio interface means for high bandwidth service connections.